1. Field of the Invention
The present invention relates to internal combustion engines for vehicles or the like, and more particularly, to a method for detecting a failure of injection fuel heaters provided in a fuel injection system of an internal combustion engine.
2. Description of the Prior Art
In order to preserve the atmospheric environment, modern internal combustion engines for vehicles or the like are equipped with injection fuel heaters in the fuel injection system thereof, whereby in the cold start of the engine the fuel heaters are operated, so that the fuel injected into the intake port or the combustion chamber is better atomized for a better combustion, so that thereby the emission of CO and HC by the exhaust gas of the engine is decreased as much as possible.
The fuel heaters are provided each at a housing portion of a fuel injection valve or at a fuel supply passage for supplying fuel to the fuel injection valve at a position adjacent its entrance, the fuel injection valves being provided each for each cylinder of the engine. The fuel heaters are each adapted to heat the fuel to be injected by a heat generated therein according to an electric resistance or an electromagnetic induction.
Those heaters are operated under such severe conditions of the engine that they are constantly subjected to violent vibrations and high temperatures, and are therefore not free from failure. It is desirable that, when one has failed, the failure is detected without delay. Further, since the heaters are separately provided for respective cylinders, it is desirable that it is known which of them has failed.
The internal combustion engines of automobiles or the like are multi-cylinder internal combustion engines having four or more cylinders. Therefore, when the fuel heaters are provided separately at respective fuel injection valves or in the vicinity thereof for the plurality of cylinders, the same number of fuel heaters are provided as the number of cylinders. Even when those plurality of fuel heaters are manufactured according to the same design and the same production process and are mounted to one engine at the same time, it is generally not foreseen which of those plurality of heaters will fail under a synergistic influence of an unavoidable fluctuation of the finished condition of the products and a small difference of each working environment. When one of them has failed, it is important that, in addition to the fact of the failure, the failed heater is specified.
The fuel heaters herein concerned are electrically operated devices, in which the failure is generally a severance in its current conducting portion. Therefore, such a failure would be readily detected with an identification of the individual heater when a galvanometer or a similar current detecting means is provided in the current supply passage for each heater. However, it increases correspondingly substantially the cost of the internal combustion engine to provide such a current detecting means for each of a plurality of fuel heaters corresponding to the number of cylinders.
Therefore, it is an object of the present invention to detect a failure of the fuel heaters with no addition of the conventional current detection means which causes an engine cost increase, by, instead, utilizing the microcomputer of a vehicle operation control device generally mounted in the modern automobiles, with such input information available from those sensors generally already provided in those vehicles, such as an air/fuel ratio sensor or a crankshaft rotation speed sensor.
According to the present invention, the above-mentioned object is accomplished by a method for detecting a failure of heaters provided in a fuel supply system of an internal combustion engine for heating a fuel injected, characterized by detecting the failure based upon a change which occurs at least in a parameter concerned with operating conditions of the engine due to the injected fuel not having been heated to a predetermined degree of heating.
In the above-mentioned method for detecting a failure of the heaters, the change in the parameter may be an increase of air/fuel ratio of an exhaust gas of the engine as compared with a value thereof to be expected when the injected fuel has been heated to the predetermined degree of heating.
Or, in the above-mentioned method for detecting a failure of the heaters, the change in the parameter may be a change in a performance of at least one of rotational speed, rotational acceleration and changes thereof of the engine corresponding to one of cylinders thereof.
Further, in the above-mentioned method for detecting a failure of the heaters, the change in the parameter may be a substantial non difference between values of the parameter according to operations of the engine with the heater being put on and the heater not being put on, respectively.
Further, in the above-mentioned method for detecting a failure of the heaters, the change in the parameter may be a substantial difference in values thereof between cylinders of the engine.
Further, the heaters for respective cylinders of the engine may be operated with a time shift therebetween in order to detect the difference in the parameter between an operation of the engine with the heaters being put on in a predetermined manner and an operation of the engine with the heaters not being put on.
The time shift in the operations of the heaters for the respective cylinders may be such that the heaters for the respective cylinders are put on with a time shift therebetween, or the heaters for the respective cylinders are put off with a time shift therebetween.
Or alternatively, two cylinders which are most distant from one another in the phases of operation of the engine may be made a pair of cylinders, and the heaters for such pairs of cylinders may be operated with a time shift therebetween in order to detect a difference in the parameter between an operation of the engine with the heaters being operated in a predetermined manner and an operation of the engine with the heaters not being operated.
In this case, also, the time shifted operations for the respective cylinders may be such that the heaters are put on with a time shift between respective such pairs of cylinders, or the heaters are put off with a time shift between respective such pairs of cylinders.
It is in the operation of several tens of seconds from the starting of the internal combustion engine in a cold state that the operation of the fuel heaters are required and they exhibit their effects. Just after the cold start of the engine, since the temperature of the wall of the combustion chamber of the engine is low, the fuel ejected from the fuel injection valve is apt to stick to the wall surfaces of the intake port and the combustion chamber as a liquid.
When such a sticking of the fuel to the wall surfaces of the intake port and the combustion chamber occurs, the fuel-air mixture becomes correspondingly lean, so that the engine is liable to fail in starting or the rotation of the engine becomes irregular. Such a fuel sticking to those wall surfaces can be temporarily met by temporarily increasing the amount of fuel injection. However, the fuel stuck on the wall surfaces is irregularly shifted toward the exhaust port with a part thereof combusted in the meantime while other remaining in liquid, thereby in any event causing a rough rotation of the engine and a deterioration of the exhaust gas purification.
In view of the above, the fuel heater is operated so as to heat the fuel ejected from the fuel injection valve, so that the injected fuel is better atomized, suppressing the fuel sticking to the wall surfaces of the inlet port and the combustion chamber in a liquid form, so that the engine rotates smoothly with a supply of fuel and air in a stoichiometric ratio from the beginning of the engine starting, thereby also making the exhaust gas to be stoichiometric.
Nevertheless, if the fuel heater for any one of the cylinders fails, so that the fuel injected in the cylinder is not heated, a sticking of liquid fuel to the wall surfaces of the intake port and the combustion chamber will occur in the cylinder, whereby the fuel-air mixture in the particular cylinder becomes lean with a corresponding increase of the effective air/fuel ratio, with the exhaust gas from the particular cylinder being rendered to show an exhaust air/fuel ratio corresponding to the ratio of the air based components to the fuel based components in the exhaust gases being increased from the value thereof expected from the supply of air and fuel, also inducing a misfire, thereby causing a loss of the corresponding torque generation.
Therefore, if it is detected with respect to at least one parameter concerning the operating conditions of the engine such as the exhaust air/fuel ratio or the rotation angular speed of the engine that the parameter has changed from a value thereof which should be exhibited when the fuel has been heated to a predetermined degree of heating in a tendency indicating that the fuel has not been heated to the predetermined degree of heating, it can be detected that the corresponding fuel heater has failed.
Such a parameter may be the exhaust air/fuel ratio of the exhaust gas corresponding to each cylinder of the engine, and the change in the parameter may be judged by an increase of the exhaust air/fuel ratio as compared with that exhibited when the fuel has been heated to the predetermined degree of heating.
On the other hand, when the fuel heater for a certain cylinder has failed, the torque generated by the cylinder decreases correspondingly, whereby there occurs a corresponding change in the performance of rotational speed or rotational acceleration of the engine corresponding to each cylinder. Therefore, the afore-mentioned change in the parameter may be a change in the rotational speed or the rotational acceleration of the engine corresponding to each cylinder.
Further, it is possible to detect a failure occurred at a certain one of the fuel heaters by the engine being operated with the fuel heaters being put on according to a predetermined manner, while the engine is operated with the fuel heaters not being put on, thereby judging if there is no difference in the parameter.
It is considered that in the engine of the automobiles or the like having four or more cylinders each equipped with each fuel heater, the probability of a second heater going to a failure following to a failure of a first heater within a one cycle surveillance of the microcomputer such as tens to hundreds microseconds is zero. (This is not the probability of a second heater going to a failure when a failure of a first heater has been left unrepaired in spite of the failure.) Therefore, it will also be possible to detect that one of the fuel heaters has failed based upon a detection of a difference occurring in the parameter between the respective cylinders.
This concept allows a probability of detecting a failure of the fuel heaters of a multi-cylinder internal combustion engine during a normal operation of the engine with the fuel heaters being put on, without taking a period of operating the engine with the heaters being put off for the purpose of detecting a failure of the fuel sensors, when the measuring techniques of air/fuel ratio, rotational speed or rotational acceleration of the engine are further improved, thereby allowing an inspection of the fuel heaters to be made optionally during a normal operation of the engine.
Further, in case of a multi-cylinder internal combustion engine, the difference between a parameter of the engine in its operation with the fuel heaters being put on and the parameter of the engine in its operation with the fuel heaters not being put on can be more clearly detected by the fuel heaters for the respective cylinders being operated with a time shift between respective cylinders.
A method of shifting the operation of the fuel heaters for the respective cylinders in time relative to one another is to shift the time of putting on the fuel heaters for the respective cylinders, while another method is to shift the time of putting off the fuel heaters for the respective cylinders. By overlapping the results of such inspections, a failure or not of the fuel heaters will be detected at a higher precision.
Further, in case of a multi-cylinder internal combustion engine, the difference between the parameter of the engine when it is operated with the fuel heaters being put on and the parameter when the engine is operated with the fuel heaters not being put on can be more clearly detected by each two cylinders thereof most distant from one another in the phases of operation are made each pair, whereby the fuel heaters for each such pair of the cylinders are operated with a time shift against other such pairs of cylinders.
Also in this case, the time shift of the operation of each pair of fuel heaters may be effected by shifting the time of putting on of each pair of fuel heaters, or by shifting the time of putting off each pair of fuel heaters. By such a shifting of the time of effective operation of the heaters from one another, a failure or not of the fuel heaters will be detected at a higher precision.